Radiation-induced lung toxicity (RILT), leading to radiation pneumonia or fibrosis, is a primary problem of radiation therapy. The pathogenesis of RILT remains unclear. In this study, we used a rat model of RILT to examine the expression of aquaporins (AQPs) after radiation injury. Sprague Dawley rats were given a single dose of 17 Gy (dose rate of 3.0 Gy/min) of X-irradiation to the thorax. Rats that survived acute pneumonitis (at 1–4 weeks) were evaluated weekly for the expression of AQP1 and AQP5 in the lung by immunohistochemical and reverse transcription polymerase chain reaction (RT-PCR) analyses. Immunohistochemical analysis showed that AQP1 protein was expressed in the capillary endothelium, and its level was significantly decreased after irradiation. AQP5 protein was expressed in the alveolar epithelium, and its level was increased between Days 7 and 14 after irradiation but decreased at Day 28, compared with the sham group. The RT-PCR results were consistent with the immunohistochemical analysis results. In summary, this study provides the first report of AQP1 and AQP5 expression in a model of radiation-induced pulmonary inflammation and edema. Decreased levels of AQP1 and AQP5 after irradiation suggest that these proteins play a role in the pathogenesis of RILT.